A prior folding apparatus is known from DE 38 21 442 C2, for example. A folding apparatus with a folding cylinder is described in this document as the prior art of this technology. A shell surface of the cylinder of this prior device is constructed of segments which are fixedly mounted on a frame of the cylinder, as well as of movable hoops, which bridge gaps between the segments. These hoops have two ends in the circumferential direction of the cylinder, one of which is fixedly mounted on one of the segments, while the other is adjustable with the aid of a strip which can be displaced parallel with the axis of the cylinder. A conversion of the axis-parallel adjustment movement of the strip, to a displacement of the end of the hoop, takes place with the aid of a pin, which pin is fixedly mounted on a sliding plate of the strip connected with the displaceable end of the hoop and which engages an elongated hole, that is oriented obliquely, in respect to the extension of the strip. By displacing the movable end of the hoop in the direction of the fixed end of the hoop, with the aid of this mechanism, arching of the hoop and therefore an increase of the circumference of the cylinder is achieved.
In connection with a folding apparatus described as the invention in DE 38 21 442 C2, the adjustment movement of the strip itself is driven with the aid of a planetary gear which, with the folding cylinder rotating, allows the rotation of two sun wheels which are coaxial with the folding cylinder. One of the sun wheels meshes with a plurality of intermediate wheels, which in turn mesh with pinion gears. The pinion gears are connected, fixed against relative rotation, with a helical spindle which engages a screw thread of the strip. The rotation of the spindles drives a translation of the strips.
With this construction, the hoops are compressed in the longitudinal direction if the circumference is to be increased. Since the hoops or bows must have a degree of stiffness, which is not negligible, in order not be deformed during contact with the material to be processed during the operation of the folding apparatus, a considerable force is required to accomplish this compression. In most cases, an adjustment movement requires a multitude of revolutions of the spindle.
DE 197 55 428 A1 describes a device for displacing two cylinder bodies of a folding cylinder by the use of a harmonic drive mechanism.